This invention relates to the preparation of xcfx89-[N-(2-aminoethyl)]aminoalkylalkoxysilanes. More specifically, this invention relates to the preparation of such silanes by reaction of xcfx89-chloroalkylalkoxysilane with excess ethylenediamine utilizing a recycled ethylenediamine hydrochloride salt phase stream.
As is well known, xcfx89-[N-(2-aminoethyl)]aminoalkylalkoxysilanes have the general formula,
R1R2NCH2CH2NR3R4
in which R1, R2, and R3 independently are a member selected from the group consisting of a hydrogen atom or an alkoxysilane of the formula:
R5Si(R6)3xe2x88x92a(OR7)a
xe2x80x83in which R5, R6, and R7 are each independently C1-8 alkyl (including straight chain or branched alkyls) and a as 1, 2, or 3. R4 is a said alkoxysilane. The xcfx89-[N-(2-aminoethyl)]aminoalkylalkoxysilanes are widely used as silane coupling agents and are effective for various polymer property modification purposes, for example, improving adhesion at an organic-inorganic interface.
These compounds are synthesized by reacting xcfx89-chloroalkylalkoxysilanes with ethylenediamine to form xcfx89-[N-(aminoethyl)]aminoalkylalkoxysilanes. Stoichiometrically, this method uses one mole of xcfx89-chloroalkylalkoxysilane and two moles of ethylenediamine for synthesizing one mole of xcfx89-[N-(2-aminoethyl)]aminoalkylalkoxysilane, with one mole of ethylenediamine monohydrochloride being formed at the same time, as shown by the following reaction scheme.
ClR5Si(R6)3xe2x88x92a(OR7)a+2NH2CH2CH2NH2xe2x86x92NH2CH2CH2NHR5Si(R6)3xe2x88x92a(OR7)a+NH2CH2CH2NH3+Clxe2x88x92
In the above equation R5 is any alkyl group and each of R6 and R7 is an alkyl radical having 1 to 8 carbon atoms and a is equal to 1, 2, or 3.
In reality, the end product xcfx89-[N-(2-aminoethyl)]aminoalkylalkoxy-silane further reacts with the starting reactants xcfx89-chloroalkylalkoxysilane and ethylenediamine to form poly-alkylated products as shown below.
ClR5Si(R6)3xe2x88x92a(OR7)a+NH2CH2CH2NHR5Si)
(R6)3xe2x88x92a(OR7)a+NH2CH2CH2NH2xe2x86x92NH2CH2
CH2N[R5Si(R6)3xe2x88x92a(OR7)a]2 
{or (OR7)a(R6)3xe2x88x92aSiR5NHCH2CH2NHR5Si(R6)3xe2x88x92a
(OR7)a}+NH2CH2CH2NH3+Clxe2x88x92
This di-alkylated ethylenediamine continues to react with xcfx89-chloroalkylalkoxysilane and ethylenediamine to form the tri-alkylated product as shown below:
NH2CH2CH2N[R5Si(R6)3xe2x88x92a(OR7)a]2 
{or (OR7)a(R6)3xe2x88x92a
SiR5NHCH2CH2NHR5Si(R6)3xe2x88x92a(OR7)a}+ClR5
Si(R6)3xe2x88x92a(OR7)a+NH2CH2CH2
NH2xe2x86x92(OR7)a(R6)3xe2x88x92aSiR5NHCH2CH2N[R5
Si(R6)3xe2x88x92a(OR7)a]2+NH2CH2CH2NH3+Clxe2x88x92
Theoretically, this process continues until a hexa-alkylated ethylenediamine product is formed, but in actuality only the mono-, di-, and tri-alkylated products are seen in detectable levels using gas chromatography analysis.
In general, a present method for preparing xcfx89-[N-(2-aminoethyl)]aminoalkyl-alkoxysilanes in a continuous flow process is as follows.
An ethylenediamine stream is co-fed to a reactor with an xcfx89-chloroalkylalkoxysilane stream of the formula:
ClR5Si(R6)3xe2x88x92a(OR7)a
as defined above, at a feed ratio of 3-20 moles of ethylenediamine per mole of xcfx89-chloroalkylalkoxysilane. The optimum molar feed ratio of ethylenediamine to alkoxysilane is dependent upon the specific alkoxysilane used. Typically the molar feed ratio just inside the single phase region is optimum, but also depends upon the desired level of polyalkylated ethylenediamines in the product.
The ethylenediamine and xcfx89-chloroalkylalkoxysilane react as described above. A single phase effluent stream from the reactor (continuous stirred tank reactor, plug flow reactor, or combination of the two), which is a mixture of ethylenediamine, alcohol, xcfx89-[N-(2-aminoethyl)]aminoalkylalkoxysilane, and ethylenediamine monohydrochloride, is passed to a stripping and/or distillation column. In the stripping column enough ethylenediamine is removed overhead to induce a phase separation in the material remaining in the column into two liquid phases.
The alcohol mentioned above is generated in a side reaction between extraneous water impurity that enters with both the ethylenediamine and the alkoxysilane feeds. The side reaction is shown below, where b is equal to or less than a and a is equal to 1, 2, or 3.
xcx9cSi(R6)3xe2x88x92a(OR7)a+b*H2Oxe2x86x92xcx9cSi(R6)3xe2x88x92a(OR7)axe2x88x92b(OH)b+b*R7OH
The two-phase effluent stream from the distillation column is passed to a phase separator (gravity, mechanical, electrical, etc.) where the denser phase which is a mixture of ethylenediamine and ethylenediamine monohydrochloride is removed.
The lighter silane phase effluent stream from the phase separator which is mainly a mixture of ethylenediamine, alcohol, and 3-[N-(2-aminoethyl)]aminoalkylalkoxysilane, is passed to a second distillation column where the aminoethylaminoalkylalkoxysilane is purified. The ethylenediamine and alcohol are removed from the top of the column and recycled to an ethylenediamine purification column that may also treat incoming ethylenediamine. The aminoethylaminoalkoxysilane stream is sometimes further purified in a stripping, distillation, or flash system to reduce the level of poly-alkylated ethylenediamine.
The ethylenediamine overhead stream and new ethylenediamine are also directed to the ethylene purification distillation column where alcohol is removed.
While producing a high yield of high quality alkylated ethylenediamines the prior process requires, as described above, that the contents of the reactor, the reaction mixture, be passed through a distillation column for removal of a substantial amount of ethylenediamine. The distillation operation was required before the residual reaction mixture could be separated into a product rich phase for product isolation and purification. It would be more efficient and economical to have a process in which the reaction mixture comprises two phases so that the product rich phase could be obtained without a preliminary distillation step and use of distillation equipment for that purpose. It is an object of this invention to provide such a process.
The reaction between two moles of ethylenediamine and one mole of a suitable xcfx89-chloroalkylalkoxysilane produces an xcfx89-[N-(2-aminoethyl)]aminoalkylalkoxysilane and a mole of ethylenediamine hydrochloride. As stated above a considerable excess of ethylenediamine is used to suppress the formation of polysilane, i.e., poly-alkylated ethylenediamine, containing products. Therefore, in a continuous process utilizing this practice, the excess ethylenediamine must be separated from the product stream and recycled to the reactor. In accordance with this invention, the byproduct ethylenediamine hydrochloride salt is also recycled to the reactor in sufficient quantity to produce two liquid phases in the reactor and in the stream flowing from it.
The two liquid phase effluent from the reactor is a mixture of xcfx89-[N-(2-aminoethyl)]aminoalkylalkoxysilane, ethylenediamine, ethylenediamine hydrochloride, and extraneous alcohol. The stream is first conducted to a phase separation vessel rather than to a distillation column. Upon phase separation, the top bulk phase contains predominantly silane and ethylenediamine. The heavier bulk phase contains predominantly ethylenediamine hydrochloride and ethylenediamine. The heavier phase is recycled to the reactor in sufficient quantity to maintain the two phase system in the reactor and used to control the degree of polyalkylation. The balance of the heavier phase is removed from the process.
The lighter phase is transferred to a purification system consisting of a distillation and/or a flash system where xcfx89-[N-(2-aminoethyl)]aminoalkylalkoxysilane(s) is purified by removal of the lower boiling species. Thus, the silane product is recovered in good yield and quality while the ethylenediamine is further purified by a second distillation and returned to the two phase system reactor.
The reaction is preferably conducted at a temperature in the range of about 60xc2x0 to 200xc2x0 C. The molar ratio of total ethylenediamine to the alkoxysilane in the reactor, including the ethylenediamine hydrochloride recycle, is at least 3 to 1 and no greater than 40 to 1.
The process of this invention is particularly useful in the manufacture of 3-[N-(2-aminoethyl)]aminopropylalkoxysilanes and 3-[N-(2-aminoethyl)]aminoisobutylalkylalkoxysilanes. For example, 3-[N-(2-aminoethyl)]aminopropyltrimethoxysilane (or -triethoxysilane) or 3-[N-(2-aminoethyl)]aminoisobutylmethyldimethoxysilane (or -methyldiethoxysilane) can be made in high yield and quality. Depending upon product requirements these silanes can be made substantially as the mono-alkylated ethylenediamines or as mixtures of predominately the mono-alkylated product with some amounts of the di-and tri-alkylated products.